Flexible tube insertion device, insertion control device, and insertion method

Abstract

A flexible tube insertion device includes a flexible tube section, at least one variable stiffness unit, at least one state detector, and a stiffness controller. The flexible tube section is segmented along an axial direction into segments and configured to be inserted into an insertion target. The variable stiffness unit is configured to vary bending stiffness of the flexible tube section in units at least one segment. The state detector is configured to detect information relating to shape information of the flexible tube section. The stiffness controller is configured to cause the variable stiffness unit to reduce bending stiffness of a portion of the flexible tube section including a place where the flexible tube section is easy to bend in units of at least one segment based on the shape information.

What is claimed is: 
     
       1. A flexible tube insertion device comprising:
 a flexible tube segmented along an axial direction into two or more segments, the flexible tube being configured to be inserted into an insertion target; 
 a variable stiffness actuator configured to vary bending stiffness of each of the two or more segments of the flexible tube; 
 and 
 a controller comprising hardware, the controller being configured to:
 acquire shape information of the flexible tube; 
 calculate a bending moment of the flexible tube in each of the two or more segments based on the shape information; 
 set a base point of variation in the bending stiffness to a segment of the two or more segments based on the calculated bending moment; and 
 cause the variable stiffness actuator corresponding to at least the segment of the two or more segments to vary the bending stiffness. 
 
 
     
     
       2. The flexible tube insertion device according to  claim 1 , wherein:
 the segment of the two or more segments including a point at which the flexible tube has a larger bending moment than at a point in other segments of the two or more segments, and 
 the controller causes the variable stiffness actuator corresponding to at least the segment of the two or more segments to reduce the bending stiffness. 
 
     
     
       3. The flexible tube insertion device according to  claim 2 , wherein:
 the segment of the two or more segments including a point in the flexible tube at which the bending moment indicates a local maximum value; and 
 the controller causes the variable stiffness actuator corresponding to at least the segment of the two or more segments to reduce the bending stiffness. 
 
     
     
       4. The flexible tube insertion device according to  claim 1 , wherein
 the segment of the two or more segments including a point at which a distance from a virtual line is longer than a distance from the virtual line to a point in other segments of the two or more segments; 
 the controller causes the variable stiffness actuator corresponding to at least the segment of the two or more segments to reduce the bending stiffness, and 
 the virtual line being orthogonal to a tangent line to a shape of the flexible tube corresponding to a position of a bend in the insertion target, and the virtual line passing through the position of the bend in the insertion target. 
 
     
     
       5. The flexible tube insertion device according to  claim 4 , wherein the distance from the point on the segment of the two or more segments to the virtual vertical line is a maximum value as compared to the other segments of the two or more segments. 
     
     
       6. The flexible tube insertion device according to  claim 1 , wherein the controller is further configured to calculate a bending moment based on the shape information to calculate a position of a point at which the bending moment indicates a local maximum value. 
     
     
       7. The flexible tube insertion device according to  claim 1 , wherein the controller causes the variable stiffness actuator corresponding to the segment of the two or more segments to vary the bending stiffness of a base point peripheral portion including a point at which the bending moment indicates a local maximum value so that the bending stiffness is lower than an initial value. 
     
     
       8. The flexible tube insertion device according to  claim 1 , wherein the controller is further configured to determine a timing for varying the bending stiffness based on the shape information. 
     
     
       9. The flexible tube insertion device according to  claim 8 , wherein the controller is further configured to:
 calculate a bending moment based on the shape information to calculate a position of a point at which the bending moment indicates a local maximum value, and 
 start the variation in the bending stiffness when the calculated bending moment is greater than or equal to a predetermined threshold value. 
 
     
     
       10. The flexible tube insertion device according to  claim 9 , wherein the controller stops the variation in the bending stiffness when the calculated bending moment is less than the predetermined threshold value. 
     
     
       11. The flexible tube insertion device according to  claim 9 , wherein the threshold value can be freely determined. 
     
     
       12. The flexible tube insertion device according to  claim 8 , further comprising:
 a bendable section connected to the flexible tube at a distal end side of the flexible tube, the bendable section being configured to actively change a bent shape, and 
 at least one first force sensor arranged in the flexible tube and at least one second force sensor arranged the bendable section, the first and second force sensors being configured to detect an external force exerted on the flexible tube and on the bendable section, respectively; wherein 
 the controller starts the variation in the bending stiffness when a contact pressure exerted on the flexible tube and the bendable section is greater than or equal to a predetermined threshold value, based on contact pressure information of the flexible tube and the bendable section that is calculated based on information obtained by the first and second force sensors. 
 
     
     
       13. The flexible tube insertion device according to  claim 12 , wherein the controller stops the variation in the bending stiffness when the contact pressure exerted on the flexible tube and the bendable section is less than the predetermined threshold value, based on the contact pressure information of the flexible tube and the bendable section so that the controller stops varying the bending stiffness at the determined timing. 
     
     
       14. The flexible tube insertion device according to  claim 12 , wherein the threshold value can be freely determined. 
     
     
       15. The flexible tube insertion device according to  claim 1 , further comprising a bent shape sensor configured to measure a bent shape of the flexible tube and input the bent shape as the shape information to the controller. 
     
     
       16. An insertion control device for a flexible tube segmented along an axial direction into two or more segments, the flexible tube being configured to be inserted into an insertion target, the insertion control device comprising:
 a controller comprising hardware, the controller being configured to:
 acquire shape information of the flexible tube; 
 calculate a bending moment of the flexible tube in each of the two or more segments of the flexible tube based on the shape information; 
 set a base point of variation in a bending stiffness to a segment of the two or more segments based on the calculated bending moment; and 
 cause a variable stiffness actuator corresponding to at least the segment of the two or more segments to vary the bending stiffness. 
 
 
     
     
       17. An insertion method of a flexible tube into an examination target, the flexible tube being segmented along an axial direction into two or more segments, the insertion method comprising:
 inserting the flexible tube into the examination target; 
 acquiring shape information of the flexible tube; 
 calculating a bending moment of the flexible tube in each of the two or more segments of the flexible tube based on the shape information; 
 setting a base point of variation in a bending stiffness to a segment of the two or more segments based on the calculated bending moment; and 
 varying a stiffness of at least the segment of the two or more segments.